1. Field of the Invention
The present invention relates to current-perpendicular-to-plane (CPP) thin-film magnetic heads, which allow sense current to flow in a film-thickness direction (a direction orthogonal to a film surface).
2. Description of the Related Art
Giant magnetoresistive (GMR) elements and tunneling magnetoresistive (TMR) elements for use as thin-film magnetic head elements are broadly divided into current-in-plane (CIP) elements and current-perpendicular-to-plane (CPP) elements. CIP elements allow sense current to flow in parallel with the surfaces of individual layers constituting the elements, while CPP elements allow sense current to flow in a direction perpendicular to the surfaces of the individual layers constituting the elements.
FIG. 12 is a sectional view of the structure of a known CPP thin-film magnetic head. This CPP thin-film magnetic head includes a lower shield layer 110, an upper shield layer 130 formed at a predetermined shield distance R-GL from the lower shield layer 110, a thin-film magnetic head element 120 formed between the shield layers 110 and 130 and exposed at a surface of the head facing a recording medium, and an insulating layer 140 formed between the shield layers 110 and 130 at the rear of the thin-film magnetic head element 120 in a height direction. The upper shield layer 130 is separated into a first upper shield layer segment 131 positioned above the thin-film magnetic head element 120 and a second upper shield layer segment 132 positioned at the rear of the thin-film magnetic head element 120 in the height direction. The second upper shield layer segment 132 is electrically connected to the lower shield layer 110 through a contact hole 141 provided in the insulating layer 140. The first upper shield layer segment 131 and the thin-film magnetic head element 120 are separated by a nonmagnetic metal layer 151, while the second upper shield layer segment 132 and the lower shield layer 110 are separated by another nonmagnetic metal layer 152. These nonmagnetic metal layers 151 and 152 are made of a nonmagnetic metal material with lower specific resistance than the shield layers 110 and 130. Shield seed layers (not shown in the drawings) are formed beneath the shield layers 110 and 130.
Sense current I flows from the first upper shield layer segment 131 to the second upper shield layer segment 132 through the nonmagnetic metal layer 151, the thin-film magnetic head element 120, the lower shield layer 110, and the nonmagnetic metal layer 152. Alternatively, the sense current I flows from the second upper shield layer segment 132 to the first upper shield layer segment 131 through the nonmagnetic metal layer 152, the lower shield layer 110, the thin-film magnetic head element 120, and the nonmagnetic metal layer 151.
An example of such a known CPP thin-film magnetic head is disclosed in Japanese Unexamined Patent Application Publication No. 2002-150518.
In the head structure described above, however, the insulating layer 140 at the rear of the thin-film magnetic head element 120 in the height direction has a large thickness, namely about 50 nm, in order to prevent a short between the shield layers 110 and 130. The insulating layer 140 therefore obstructs the dissipation of heat generated from the thin-film magnetic head element 120 and the shield layers 110 and 130, thus impairing heat dissipation properties.
In the above head structure, as is well known, the shield layers 110 and 130 are made of a soft magnetic material such as NiFe. When, therefore, the sense current I flows through the shield layers 110 and 130, they cause an anisotropic magnetoresistance (AMR) effect. This effect decreases the resistance of the shield layers 110 and 130, and thus causes noises in the output of the thin-film magnetic head element 120. In particular, the current density is higher in regions where the sense current I enters or exits the shield layers 110 and 130. In these regions, therefore, the AMR effect generates a larger amount of noise. The noise due to the AMR effect can be reduced by forming the shield layers 110 and 130 with a shield material having a smaller AMR effect. Such a shield material, however, cannot produce a sufficient magnetic shield effect. Alternatively, the current flowing through the shield layers 110 and 130 can be reduced by increasing the thicknesses of the nonmagnetic metal layers 151 and 152. The increased thicknesses, however, result in a longer shield distance R-GL between the shield layers 110 and 130, and therefore make it difficult to reduce the shield distance R-GL.